1. Field of the Invention
The present invention relates to the field of network communication technologies, more particularly to a method for forwarding multicast message in network communication.
2. Background of the Invention
With the large-scale use of meeting TV and development of IPv6, the multicast technology has been used more and more popularly. Multicast message forwarding is usually realized by IGMP (Internet Group Management Protocol) in combination with multicast routing protocol. The concrete method is to run the multicast routing protocol on every router in the multicast network, the multicast routing protocol can be any of DVMRP (Distance Vector Multicast Routing Protocol), PIM-DM (Protocol-Independent Multicast—Dense Mode), CBT (Core Broadcast Tree) or PIM-SM (Protocol-Independent Multicast—Sparse Mode). For the routers on the domain boundary and hosts that are required to join the multicast group, IGMP also has to be run. The host sends a request of joining the multicast group through IGMP, and the router connected to the host joins corresponding port of the host to a responding multicast group after receiving the request. Inside the multicast network, the multicast routing protocol forms the multicast forwarding routing table according to topology of the interface joining the multicast group. When the source port sends a message whose destination address is a multicast IP address to the multicast network, the router in multicast network forwards it according to the multicast routing table formed by the multicast routing protocol. After the message has been forwarded to the router connected to the host, the router sends the message in multicast mode to the interface where the host is connected.
In the network as shown in FIG. 1, the multicast source (Source) connects to the multicast network through Router1. Router1, through domain formed by a plurality of routers, connects to Router2 on the domain boundary. Router 2 connects to the host PC1 through Ethernet and the host PC2 is also in Ethernet. In order to correctly forward the multicast message from Source to PC1, the traditional method needs at least the following configuration: a kind of multicast routing protocol in dense or sparse mode has to be run on every router in the multicast network; router-side application of IGMP is run on the routers (Router2, Router3) on the domain boundary in the multicast network; client-side application of IGMP is run on the host requiring multicast.
After configuring as above, in order to forward the multicast messages normally, it also need the multicast routing protocol messages, transferring multicast routing information, transferred regularly between the routers in the multicast network, as well as the regular report message and the join/leave message in the announce state between the routers on the domain boundary and the host. As is shown in FIG. 1, first, PC1 sends the join message to Router2 for applying for joining in the multicast group, Router2 joins the Ethernet interface that PC1 corresponds to in the multicast group, and the join message propagates in the whole multicast network through multicast routing protocol messages, and forms the multicast routing information which can be used to send the message to the bearer multicast message interface. In this way, when Source sends a multicast message meeting requirements through Router1, the forwarded messages through the multicast network are sent to Router2 on the domain boundary, and Router2 sends the multicast message to the Ethernet interface connected to PC1, which receives the message.
Seen from conventional technical scheme, conventional multicast routing forwarding method has the following problems: first, it lowers the security of IP message, the security is not very high originally. When the router sends a multicast message to the used host, IGMP sends message from the interface in multicast mode, while in broadcast-type networks (such as Ethernet), this sending mode will cause the problem that the message is sent to the host which should not receive it originally. As is shown in FIG. 1, host PC2 can also receive the multicast message intended for PC1. This mechanism sometimes restrains the application of multicast to a great extent. Second, the inconvenience of the traditional method lies further in the fact that the network configuration is quite troublesome, there are various configurations for hosts, routers on the boundary and forwarding routers and it involves client-side application and the router-side application of the multicast routing protocol and IGMP, demanding a higher qualification from the network administrator. Third, running the multicast routing protocol on all routers will affect the forwarding efficiency of the routers and increase the burden on the routers and hosts in the multicast network. Fourth, a great deal of multicast protocol messages generated between routers and between hosts and routers in the multicast network occupy precious bandwidth resource.